It is well known that contact lenses can be used for cosmetics and the correction of visual acuity. The ideal contact lens is one which is not only comfortable to wear for extended periods of time, but also easily and reproducibly manufactured at minimum cost in time and labor.
European Patent EP 0 637 490 B1 describes a process by means of which a further improvement in the production process of contact lenses from crosslinkable prepolymers, such as, for example, water-soluble crosslinkable polyvinyl alcohols described in U.S. Pat. Nos. 5,508,317, 5,583,163, 5,789,464 and 5,849,810 and water-soluble crosslinkable polyurea prepolymers described in U.S. Pat. No. 6,479,587, can be achieved. In this case, a lens-forming material (a prepolymer solution) is introduced into a mold consisting of two mold halves, the two mold halves not touching each other but having a thin gap of annular design arranged between them. The gap is connected to the mold cavity, so that excess lens forming material can flow away into the gap. The crosslinking of the lens-forming material in the mold cavity is carried out by means of actinic irradiation, in particular UV light, under spatial limitation of actinic irradiation (e.g., by means of a chromium mask). Thus, only the lens-forming material which is in the unmasked area in the mold cavity is crosslinked, whereas the lens-forming material located in the masked area (behind the mask, such as in the gap). High reproducibility of the rim shaping of the lens can be achieved without a positive connection between the two mold halves made of polypropylene or polystyrene. The uncrosslinked, shadowed prepolymer solution can easily be washed away from the dimensionally stable, crosslinked lens by using a suitable washing media (e.g. water). Instead of polypropylene or polystyrene molds that can be used only once, it is possible to use reusable quartz/glass molds or reusable plastic molds, since, following the production of a lens, these molds can be cleaned rapidly and effectively of the uncrosslinked prepolymer and other residues, using water, on account of the water-soluble basic chemistry, and can be blown dried with air. By this means, high volume molding of contact lenses with high precision and reproducibility can in particular be achieved.
Contact lenses produced from the above-described water-soluble crosslinkable prepolymers have advantageous properties such as a good compatibility with the human cornea resulting in a high wearing comfort and the absence of irritation and allergenic effects. However, contact lenses made from those water-soluble photo-crosslinkable prepolymers may not always posses combination of most desirable physical/mechanical properties, for example, such as tensile properties (stress at break, elongation at break, and modulus), water contents, biocompatibility, for the intended uses, tensile properties (stress at break, elongation at break, and modulus).
Accordingly, there is still a need for a new prepolymer for economically producing durable, highly elastic soft contact lenses with desired physical/mechanical properties.